Electrode structure for electric discharge devices



18, 1951 L. J. DAVIES ET AL 2,579,109

ELECTRODE STRUCTURE FOR ELECTRIC DISCHARGE DEVICES Filed Jan. 10, 1950 Invervtovs: Leonard J. Davies, Evi'c J.G.Beeson,

b5 m I Their A k ovneg.

Patented Dec. 18, 1951 ELECTRODE STRUCTURE FOR ELECTRIC DISCHARGE DEVICES Leonard J. Davies, Rugby, and Eric J. G. Beeson,

Southwell, England. assignors to General Electric Company, a corporation of New York Application January 10, 1950, Serial No. 137,788 In Great Britain January 25, 1949 2 Claims.

This invention relates to electrode Structures for electric discharge devices, particularly electric discharge lamps of the compact source type, that is, of the kind in which relatively massive electrodes are employed which are spaced a few millimeters apart in an envelope, the diameter of which is great compared with the arc length, the envelope containing a filling of rare gas and a vaporizable substance, such as mercury, or gases capable of providing, during operation, a pressure of many atmospheres.

It is known that such lamps may be operated at different levels of power consumption by control of impedance in series with the lamp. It has been usual to design the lamp as if it were intended for operation at the higher level of power consumption and to operate it at a greatly reduced level, generally referred to as simmering only when the full light output is not required. When the periods of maximum power consumption are of short duration and constantly recurring, as when the lamp is used for the purposes of signalling by the Morse code, the maximum level of power consumption may be such as, if continuously used, to result in the destruction of the lamp by overheating of the electrodes, particularly the anode.

It is the object of the present invention to provide a construction for the anode which will enable the lamp to be overrun for longer periods without resulting in the destruction of the lamp, whereby a smaller lamp may be employed for any given duty.

According to the invention the anode of an electric discharge lamp of the kind set forth above is made of two metals, in intimate thermal relation, the outer surface layer which is exposed to the bombardment by the arc discharge being constituted of a highly refractory metal having a relatively low thermal conductivity, such as tungsten or molybdenum, while the underlying metal not exposed to the action of the are discharge is constituted of a metal of lower melting point than that mentioned above but possessing a high thermal conductivity, such as copper, which is preferably extended through the wall of the envelope whereby to faciltate the removal of heat therefrom.

In carrying out the invention, the lamp may have an anode consisting ofa hollow part made of tungsten or other suitable refractory material by the method disclosed in British Patent No. 555,344, the inside of which is filled with copper or other suitable metal of high thermal conductivity, such as silver. The copper or equivalent metal is caused to be in intimate contact with the surrounding wall of tungsten, and to give the best results is melted in vacuo into the tungsten, and the thickness of the tungsten is carefully controlled as to represent the minimum thickness consistent with mechanical strength and freedom from such troubles as would be caused by the penetration of mercury through the tungsten to the copper. Copper also has the advantage of possessing high thermal capacity and the mass of copper thus serves to remove heat from the surface layer of tungsten and keep it relatively cool.

If necessary, the lead-in conductor to the anode can be made hollow also, and the copper filling extended through the hollow lead-in to the outside of the envelope, where it can be the effective face of the anode, and the rim being sealed to the envelope by a ring seal. The interior of the cup is occupied by a mass of copper or similar good heat and electrically conducting metal, which extends outwardly from the cup and is formed into a terminal by which connection from the supply to the anode is made. The extending portion of the copper may be provided with radiating fins to assist in the dissipation of heat from the anode, or the copper may be provided with a cavity into which cooling fluid can be introduced. If desired, there may surround the outwardly extending portion of the anode a strengthening member (either of the vitreous material or met ll) which surrounds the seal to the tungsten portion of the anode and. being sealed to the envelope and the anode, serves to provide additional rigidity and relieve the tungsten seal of externally applied stress.

Alternatively, the rim of the tungsten cupshaped portion of the anode may be secured,

as by welding, to an annular metal disc of a metal or alloy, such as molybdenum, which is capable of being sealed more readily to the vitreous material, usually quartz, of which the lamp is composed.

For a further understanding of the invention reference may be had to the drawing which is an elevation, partly in section, of a portion of a lamp including an anode structure embodying the invention.

Referring to the drawing, the anode I comprises a sheet or shell 2, of tungsten for example, having a reduced cylindrical portion 3 extending from the open end thereof. The anode is sealed to the quartz bullor envelope 4 by a ring seal in the form of a thimble or ferrule 5, of molybdenum for example, having a feathered edge 6 embedded'in the neck portion 1 of the bulb I, the cylindrical portion 3 of the anode extending through a central aperture in the thimble and being hermetically united thereto at 8 by a suitable brazing metal or alloy or a seal of glass or other vitreous material. The interior of the shell 2 is filled with a mass of copper 9 or equivalent metal which extends outwardly through the cylindrical portion 3 and terminates in a terminal contact portion 10. The outwardly extending portion of the copper core 8 may be provided with radiating fins H to assist in dissipating heat from the anode.

While the construction forming the subject of the present application has been described in its application to the anode of an electric discharge lamp, a similar construction may be adopted for the cathode of the lamp, should this appear desirable.

The improved lamps according to the invention are particularly suitable for projection, photography, and the illumination of cinema studios and the like. The scene to be photographed is thus illuminated by the lamp 0perated at its lower power consumption (in which conditions the lamp will have a long life), and when photographing is required, the power consumption is increased to the maximum value, whereupon the photographing of the scene can be effected. Since the same light source is used both for the preliminary arranging of the scene andfor its photographing, the position of the light source, in both cases, remains unchanged.

A lamp of smaller bulk and therefore requiring' a smaller lantern and operating equipment can be employed, since the useful life, during its maximum power consumption conditions, is still considerable.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a high intensity electric discharge lamp, the combination of an envelope of vitreous material, and electrode sealed in an end of said envelope and comprising a hollowshell portion of highly refractory metal of the group consisting of tungsten and molybdenum, said shell portion being hermetically sealed to the wall of said vitreous envelope, a core portion within said shell and in intimate thermal contact therewith (to assist in removal of heat from said shell, said core portion consisting of metal of the group consisting of copper and silver, and means supplementary to said shell and core for removing heat from said core and dissipating it exteriorly of the lamp.

2. In a high intensity electric discharge lamp, the combination of an envelope of vitreous ma- 'terial, an electrode sealed in an end of said envelope and comprising a hollow shell portion of high refractory metal of the group consisting of tungsten and molybdenum, said shell portion being hermetically sealed to the wall of said vitreous envelope, a core portion within said shell and in intimate thermal contact therewith to assist in removal of heat from said shell,

said core portion consisting of metal of the group consisting of copper and silver, an annular ring member of molybdenum sealing said electrode to said envelope and having its inner rim hermetically secured to said shell portion and an outer rim of tapered thickness which is embedded in the material of said envelope, and means supplementary to said shell and core for removing heat from said core and dissipating it exteriorly of the lamp.

LEONARD J. DAVIES.

E. J. G. BEESON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,046,083 Kraus et a1. Dec. 3, 1912 1,662,891 Mutscheller Mar. 20, 1928 1,953,813 Matsushima Apr. 3, 1934 2,276,046 Kilgore et a1. Mar. 10, 1942 

